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Message-ID: <55A5839F.8060608@fb.com> Date: Tue, 14 Jul 2015 15:48:15 -0600 From: Jens Axboe <axboe@...com> To: Mike Snitzer <snitzer@...hat.com> CC: <linux-kernel@...r.kernel.org>, <hch@....de> Subject: Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB On 07/14/2015 02:45 PM, Jens Axboe wrote: > On 07/14/2015 02:44 PM, Mike Snitzer wrote: >> On Tue, Jul 14 2015 at 2:48pm -0400, >> Jens Axboe <axboe@...com> wrote: >> >>> Lots of devices exhibit very high latencies for big discards, hurting >>> reads and writes. By default, limit the max discard we will build to >>> 64MB. This value has shown good results across a number of devices. >>> >>> This will potentially hurt discard throughput, from a provisioning >>> point of view (when the user does mkfs.xfs, for instance, and mkfs >>> issues a full device discard). If that becomes an issue, we could >>> have different behavior for provisioning vs runtime discards. >>> >>> Signed-off-by: Jens Axboe <axboe@...com> >> >> Christoph suggested you impose this default for the specific >> drivers/devices that benefit. I'm not following why imposing a 64MB >> default is the right thing to do for all devices. > > I'd argue that's most of them... But the testing we did was on NVMe. I > can limit it to NVMe, no big deal. Oh, and LSI flash too, so not just NVMe. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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